wireform

A json.dumps drop-in that serializes dataclasses, datetime, Decimal, bytes, sets, exceptions, and anything that implements __repr_in_dumps__.

Installation

pip install wireform

Requires Python 3.11+.

Why wireform?

The stdlib json.dumps refuses most real-world Python values:

• json.dumps(MyDataclass(...)) → TypeError — dataclasses are not serializable out of the box.
• json.dumps(datetime.now()) → TypeError; same for date, time, Decimal, bytes, set, frozenset, exceptions, and class objects.
• Silently accepting naive datetime is a trap — the reader can't tell if the timestamp is UTC or local. wireform refuses naive datetimes by design.
• dataclasses.asdict exists, but doesn't respect field(repr=False) and can't coexist with custom encoders for other types.

custom_dumps is a single callable that handles all of these without schemas, models, or configuration.

Quick Start

import datetime
from dataclasses import dataclass
from decimal import Decimal

from wireform import custom_dumps

@dataclass
class Payment:
    amount: Decimal
    currency: str
    paid_at: datetime.datetime

payment = Payment(
    amount=Decimal("19.99"),
    currency="EUR",
    paid_at=datetime.datetime(2026, 4, 18, 12, 0, tzinfo=datetime.UTC),
)

custom_dumps(payment)
# '{"amount": "19.99", "currency": "EUR", "paid_at": "2026-04-18T12:00:00+00:00"}'

custom_dumps({"tags": {"admin", "editor"}, "blob": b"hello"})
# '{"tags": ["admin", "editor"], "blob": "data:application/octet-stream;base64,aGVsbG8="}'

# Naive datetime — refused by design:
custom_dumps(datetime.datetime.now())
# TypeError: datetime.datetime WITHOUT tzinfo is not JSON serializable

Overview

Serialization: custom_dumps | EnhancedJSONEncoder | ReprInDumps

File I/O: read_json_file_by_path

Types: JsonLoaded | Jsonable | CustomJsonable | JsonDumper

---

Serialization

custom_dumps

A partial(json.dumps, cls=EnhancedJSONEncoder). Same signature as json.dumps, same return type (str), but accepts the extended set of Python values listed below.

from wireform import custom_dumps

custom_dumps({"a": 1, "b": [1, 2, 3]})
# '{"a": 1, "b": [1, 2, 3]}'

Supported values beyond stdlib JSON:

Python value	JSON representation
@dataclass instance	object of fields with repr=True (skips ClassVar, InitVar, repr=False)
datetime (tz-aware)	ISO 8601 string — "2026-04-18T12:00:00+00:00"
datetime (naive)	raises TypeError
date, time	ISO 8601 string
Decimal	string — "19.99"
bytes	data URL — "data:application/octet-stream;base64,..."
set, frozenset	JSON array (unordered)
type (class object)	{"_t": "PY::class", "key": "<qualname>"}
Exception instance	{"_t": "PY::Exception", "key": "<type qualname>", "args": [...]}
ReprInDumps subclass	value returned by __repr_in_dumps__()

EnhancedJSONEncoder

The underlying json.JSONEncoder subclass. Pass it to json.dumps(..., cls=EnhancedJSONEncoder) if you need the extra dumps kwargs directly rather than through custom_dumps.

import json
from wireform import EnhancedJSONEncoder

json.dumps({"x": {1, 2, 3}}, cls=EnhancedJSONEncoder, indent=2)

ReprInDumps

Mixin that lets a class control its own JSON form. Subclass it and either (a) override __repr_in_dumps__ to return any Jsonable value, or (b) rely on the default, which delegates to repr(self) and produces a JSON string.

from wireform import ReprInDumps, custom_dumps

class Tag(ReprInDumps):
    def __init__(self, name: str):
        self.name = name

    def __repr__(self):
        return f"Tag({self.name!r})"

custom_dumps(Tag("admin"))
# '"Tag(\'admin\')"'


class Version(ReprInDumps):
    def __init__(self, major: int, minor: int):
        self.major = major
        self.minor = minor

    def __repr_in_dumps__(self):
        return {"version": f"{self.major}.{self.minor}"}

custom_dumps(Version(1, 2))
# '{"version": "1.2"}'

File I/O

read_json_file_by_path

Open a file at the given path and parse it as JSON.

from wireform import read_json_file_by_path

data = read_json_file_by_path("config.json")

Returns a JsonLoaded — the exact tree shape you get from json.load.

Type Aliases

• JsonLoaded — the strict output shape of json.load / json.loads: list, dict[str, ...], str, int, float, None.
• Jsonable — anything the stdlib json.dumps accepts: JsonLoaded plus tuple, and dicts with int keys.
• CustomJsonable — anything custom_dumps accepts: Jsonable plus set, frozenset, bytes, ReprInDumps, type, dataclasses, datetime, date, time, Decimal, Exception.

JsonDumper

typing.Protocol matching the json.dumps signature. Use it when you want to type-hint a "something that behaves like json.dumps" parameter (e.g. to let callers swap custom_dumps for the stdlib version).

from wireform import JsonDumper, custom_dumps

def render(data, *, dumper: JsonDumper = custom_dumps) -> str:
    return dumper(data, indent=2)

A Note on Roundtripping

custom_dumps is a one-way encoder. Values like set, bytes, Decimal, class objects and exceptions are encoded to JSON-compatible forms, but json.loads will give you back the encoded shape (list, str, etc.), not the original Python type. Use wireform when you need to emit JSON — not when you need a serializer/deserializer round-trip.

License

MIT